Process for producing shaped articles of tetrafluoroethylene polymers



PROCESS FOR PRODUCING SHAPED ARTICLES OF TETRAFLUOROETHYLENE POLYMERSJames Rushton White, Chadds Ford, Pa., assignor to E. I. du Pont deNemours and Company, Wilmington, Del., a corporation of Delaware NoDrawing. Filed Dec. '12, 1957, Ser. No. 702,223

14 Claims. (Cl. 18-54) The present invention relates to a method ofextruding fluid polytetrafluoroethylene dispersions into continuousfilaments.

It is well known that polymers from tetrafluoroethylene cannot be meltspun into textile denier fibers owing to their extremely high softeningpoints and high melt viscosities. Normal dry or wet spinning is notpossible because of the lack of solubility of polytetrafluoroethylene inknown solvents. This means that polytetrafiuoroeth ylene cannot beprocessed into continuous structures by any of the conventionally knownspinning methods and only very few processes, all of them complicated,are known to produce continuous filaments from polytetrafluoroethylene.

One of these methods, described in U.S. Patent 2,685,707, to Llewellynand Lontz, utilizes a waterfree lubricated paste containingpolytetrafluoroethylene. This process, however, does not provide whitefilaments of textile denier. Another method, described in U.S. Patent2,559,750 to Berry, requires polytetrafiuoroethylene particles having acertain shape, that is, some of the dispersed polytetrafluoroethyleneparticles are in the form of rods with a certain diameter to lengthratio. Furthermore, these compositions must be extruded into acoagulating bath in order to yield filaments. Other processes, such asdescribed in U.S. Patent 2,776,465 to J. Smith and U.S. Patent 2,772,444to Burrows and Jordan, as well as British Patent 767,015, require theuse of matrix materials. In these cases, the resulting filament eitherstill contains matrix material, or, in case this matrix material hasdisintegrated at the high temperature of the sintering step for thepolytetrafiuoroethylene particles, charred particles remain to give it adark color, unsatisfactory for certain applications.

It is an object of the present invention to produce apolytetrafluoroethylene filament. It is another object to produce awhite polytetrafiuoroethylene filament. Another object is the productionof textile denier polytetrafluoroethylene filaments free of matrixmaterial. A further object is the provision of a method for theproduction of filaments, films, ribbons, tapes, etc., frompolytetrafluoroethylene particles.

These and other objects are accomplished by providing a liquid spinningmixture comprising from about 45% to about 85% by weight of dispersedparticles of a tetrafluoroethylene polymer from about 2% to about 20% byweight of dispersing agent and from to about 415% by weight of a water.soluble organic thickener' with a dispersionnumber greater than 5', forexample, s ay:

alcohol, monoether or monoester ofthe polyalcohol each? having at leasttwo free hydroxy groups, a hydroxyalkyl,

2,968,522 Patented Jan. 17, 1961 2 amine, a polyhydroxyalkyl amine,carbohydrate or bis(omega-amino-alkylene) amine, said spinning mixturebeing characterized by a total organic material content of at leastabout 70% the remaining proportion being water. This mixture is formedinto a shaped article under conditions of high shear, as, for example,by extruding through an orifice having a diameter between about 5 andabout mils and a length between about 0.5 and 5 inches, at a pressure ofbetween about 1000 pounds per square inch and about 5500 pounds persquare inch and' a temperature of between about 50 C. and about 110 C.

The resulting filament is collected preferably under tension.

Additional shear may be applied to the spinning mixture by passing itthrough a sand pack of from about 0.5 to about 1.5 inches in lengthprior to extruding through the spinning orifice. Under these conditions,a gelfilament emerges from the spinneret, which is wound up with aspin-stretch factor of up to about 1:5; i.e., the gelfilament is woundup at a rate up to 5 times as great as the spinning rate andconsequently stretched. The wound up gel-filament is washed in acetone,dried, sin tered at from about 375 C. to about 430 C. over a hotpin, anddrawn up to about 10 times its original-length;

The spinning mixtures of the present invention-are dispersions ofpolytetrafiuoroethylene. Such dispersions are prepared .by transferringcolloidal pol'ytetrafluoroethe ylene particles from an aqueous phase toanother con tinuous phase containing organic material alone or organicmaterial in combination with Water. The aqueous colloidal dispersion ofthe polymer contains from about- 2% to about 20% by weight of adispersing agent, such as Triton X-lOO, a non-ionic ethylene oxide-octylphenoldispersing agent (reaction product of 12l3 moles of ethylene oxidewith 1 mole of para-octyl phenol) and a non-ionic, water-miscibleorganic liquid which will form a continuous phase in the final mixture.Removal, as byevaporation, of part or all of the water from this mixturecontaining dispersing agent and organic liquid, produces a colloidaldispersion of polymeric particles in a continuous predominantly organicphase. The initial aqueous colloidal dispersion of polymeric tetrafluoroethylene utilized may be prepared by the processes described in U.S."Patents 2,478,229 and 2,559,752, both issued to Berry;

The organic liquid which in this embodiment forms the continuous phaseof the spinning composition of this. in ention is non-ionic andwater-miscible and has a dispersion number greater than 5, butpreferably not more. than 35. The term dispersion number, as usedherein, is the sum of the following oxygen and nitrogen values of thesaid water-soluble organic compounds: each alcoholic: oxygen=4, eachamino nitrogen=2, each ether oxy-' gen=l. Other functional groups, e.g.CO-- of alde hydes or ketones count zero. For example, by this defi-.nition triethanolamine has the dispersion number of 14; glycerin is 12,sucrose 33, aminopropa nol 6, etc. Those non-ionic, water-miscibleorganic compounds having. a, dispersion number of 5 or less, such asmethanol (disper-.' sion number=4), monoethers (dispersion numberf=l) orethylenediamine (dispersion number=4), do not pro:

vide suitable dispersions and, consequently, are not in? cluded withinthe operable range of useful compounds;

An aqueous polytetrafluoroetnyiene dispersion, such as marketed by duPont under the trade'name of TD 3, isfl readily used as the startingmaterial. This aqueous are Example I A commercial aqueouspolytetrafluoroethylene colloidal dispersion containing. 60%.:polytetrafluoroethylene and 6%:Of Triton X.- 100, describedrabove, is.heated to 90 C., centrifuged, and. Water'decanted. Theresultaut dispersiou, which contains. 69% polytetrafluoroethylene and 6% Triton. X-100,is extruded at 90 C. and at 2,000 pounds persquare inch through 0.8'inchof 150-200 mesh sand and thence through an orifice 8 mil in diameterwith a: length of 0.5. inch; The extruded filaments, having a; geltenacity of 0.0024 gram. per. denier, are dried, sintered'and. drawn.7(seven times their original length) at. 375 C. over a hot'pin to yield afilament with a tenacity'of 1.5. grams per denier.

Example II,v

To a'commercial aqueous 60% polytetrafluoro'ethylene colloidaldispersion containing 450; parts of polytetrafluoroethylene and"27'partsofTriton-X 10'0; are added l58t-partsof an organic thickener mixtureyofethylene glycol/"glycerol, of percentage composition 60/40. Thismixture-is stirred slowly in aresin kettle for several hours ata'reduced pressure of about 50mm. and aternperature arse C." When theamount of polytetrafluoroethylene in this mix has increased to about 65%through evaporation of liquid, the mixture has the followingcomposition: polytetrafluoroethylene 65 dispersing agent (Triton- X-lOO)4%, organic solvent mixture 21% and water10%-.

Example'lll The'spinning mixture of ExampleII is" heated to 90 C. pouredinto a spinning cell. It is" extruded at a pressure of. 1600,poundspersquare inch through a 0.3- inchthicksand packwhich contains150-200- mesh sand retainedbya 3.25. mesh screen, and then-through a 5hole spinneret with hypodermic needle-type orifices of 5 00 mil lengthand 8 mil diameter. The'yarn is woundup at a speed-of. 180 feet perminute. This wind-up speed is about twice the speed of extrusion. Theadditional pull reduces .the denier of the yarn and increases itstenacity. A similar'yarn which ispiddled' rather than pulled away fromthe'spinneret does not give a sintered product of appreciable strength.

The bobbin containing the gel-filaments is immersed as a. whole into anacetone bath until the glycols and dispersing agent are leached out. Itis subsequently removed from the bath and dried. The yarn is then passedover a-sintering roll at 375 C. with a contact time of 20 seconds; It iswound up with a slight draw of about 1.5'X 'to about 2X. The yarn soobtained is completely colorless. It'possesses a" cold drawability ofabout 3x and is hot drawn to 8X, to yield a .yarn having a tenacityoil-1.5" to 2.0 grams per denier.

The viscosity offthe above spinning mixture containing glycol/glycerolis such that when extrudedwithonta sand pack the mix drips out oftheorificeor orifices; withou t,

the formation. of. any fiber. This. indicates that at least part of theeffective, shearing action stems from he. sand. P k.

The viscosity of the commercial 60% polytetrafluoroethylene dispersionis" about- 24 centipoises at 0 C., dropping to about 12 centipoises at32 C. and rising sharply with increasing temperature to a maximum of 137centipoises at 80 to C. Thus, for example at 8090 C. and with a givenspinneret and pressure conditions, better spinning is obtained than attemperatures between 40 and 75 C.

Example IV To a commercial 60%v polytetrafluoroethylene colloidaldispersion containing 450 parts polytetrafluoroethylene and 27 partsof.- Triton; X-100, described above, is. added 158 parts diethyleneglycol. This mixture, is stirred at 50 C. under partial vacuum until themixture contains about 69%: polytetrafluoroethylene. The mixture; ispoured at 50 C. into a spinning. cell. equipped with two 325 meshscreens but no sandpack, and a hypodermic needle. type orifice of 250mil-length. and 8 mil diameter. The shear-coalesced gel-filament,is-wound up at a rate of 520 feet per minute, by applying a pressure ofabout 1500 p.s.i. to the spinning mixture and a spin-stretch factor ofabout .2. The filament is washed thoroughly to remove organic solventand Triton X- by repeatedly immersing the bobbin in acetone,- dried,sintered'over a hot pin at 375 C. with a contact time of 20 sec, anddrawn' 10x to a denier of 15'.

Attempts to sinter' this" gellfiber without removing the glycol'areunsuccessful because the fiber sticks to the sintering rolland is brokenup into small sections. This fragility is also observed when theunwashed'gel-filament is dried'onrthe bobbin;

Example V Following the procedure of Example. II, spinning mixtures areprepared by replacing the glycerol/ethylene glycol mixture with otherliquids. These liquids are listed below in sequence ofthickeningefiects, the best thickvarious thickeners. according to thepreviously given" dispersion numbers. Each of theseorganic liquids isadded to a separate aqueous polytetrafluoroethylene dispersion.- Eachmixture is spreadion a glass plate and the resulting films are examined.after allowing them to approach dryness. Films prepared from.dispersions containing the thickeners whose. ratings are less than 6,showsmud-cracking and have no fiber-forming; tendencies, whilethose fromdispersions containing thickeners with higher dispersion. number valuesproduce uncracked. pastefilms. The paste forming these latter. films:canbe rolledinto aball between fingers and. then. drawntout into:aifiber severalinehes; long;

Ex mples. VI to XX Several spinning dispersions, varying inpolytetrafiuoroethylene; concentrations from 45-79% and in concenetrations of; glycerol/glycol of percentage composition 6.0 4.0;areextrudedunder conditions stated in the follow ngttable.

"Teflon Triton Thiek- H40 Press Tem As-S un E1011 Example Number(percent) (percent) ener (percent) Orifice (inch) (p.s.i) 08 Tena lty(pereefit) Denier (percent) (g.p.d.)

O0ntalns 3% white oil (purified mineral oil).

The lowest extrusion pressure for producing a strength it varies withspinning conditions is qualitatively easily in the gel filament of above0.01 gram per denier is predicted. about 3,000 pounds per square lIlCh wth the above thick- 20 The energy dissipated when shearing force isapplied nerfi g P s r r found to e better teflflcltlesto a polymerincreases with increasing pressure, increas- However, gel filaments witha dry tenacity of 0.001 gram ing amount of solid particles in thedispersion, (as ex- P denier are usually Strong enough t be fi lf t0pressed by concentration), increasing size of number of furthgrProcesses, -e waslplng, y smterme and obstacles in the flow of thisdispersion (e.g., with increasdrawlng- The Preferred {nlmmum 1 tellaclty1S 25 ing orifice length), increasing length of sand pack, a ut 0-00 5gram P61 1611 11 decreasing orifice diameter, and increasingtemperature. Most of the gelled filaments listed in the table are ob-All these items are variables in the spinning process of tamed bypiddling which means that no stretch 1s exerted th present invention andare discussed below. on the gel-filament. In Examples 14 to 17inclusive, the Pressure.A minimum pressure of 1000 pounds pergel-filaments are wound up at a spin-stretch factor of square inch hasbeen found to be a practical lower limit.

about 121.5 to 1:2.

The gel-filaments of the present invention are normally washed withwater and/or acetone or other well-known water-miscible volatilesolvents to remove spinning solvent and dried. These operations can becarried out on a bobbin and no advantage is seen in carrying out theseoperations by winding them from the bobbin through a wash liquid,leading them through a drying chamber and rewinding them, unless thegel-filament is produced in a continuous process to which the presentinvention is easily adaptable.

Development of optimum mechanical properties in the filaments isdependent in part on sintering conditions, since incomplete sinteringresults in weak spots with attendant poor mechanical properties. Theoptimum sintering temperature for developing of optimum properties for apolytetrafiuoroethylene filament is from about 375 C. to about 430 C. Atthis temperature, filaments are sintered about 7 seconds to developoptimum physical properties. Sintering temperatures higher than 430 C.are undesirable becauseof degradation of the polymer, while attemperatures below about 375 C. the contact time required to developmaximum properties is excessive.

Monofilament as well as multifilament yarns can be produced by thisinvention. Individual monofilaments may be processed separately or spun,into yarns prior to processing to remove solvent, dispersion agent andthickener.

The present invention permits production of a perfectly whitepolytetrafluoroethylene filament of about one to more than two grams perdenier tenacity after conventional processing, including sintering anddrawing. The filaments from this process have high tenacity and arestrong enough to be stretched, backwound, washed, and dried before thefilament is eflectively sintered into a continuous structure. The shearcoalescing or the polytetrafluoroethylene dispersion into a gel filamentis peculiar to the polytetrafluoroethylene polymer, since other polymersdo not form a gel filament of sufficient strength to be processed whenextruded as a fluid dispersion under the conditions of the presentinvention.

Under the conditions for carrying out the present process considerableshearing force is exerted on the polymer. Shear, as it is used in thepresent process canf not readily be measured. However, the manner inwhich However, by varying other shear inducing conditions, lowerpressures might also be useful. Pressures in excess of 5500 pounds persquare inch are operable, but no great advantage in using such pressurescan be seen.

C0ncentrati0ns.-'Ihe concentration referred to is the amount of solidpolytetrafluoroethylene particles in the total amount of the fluiddispersion. It has been found that a concentration of 45% by weight ofpolytetrafluoroethylene polymer in the form of dispersed particles is alower limit when organic thickeners are provided. In a dispersion ofwater alone, at least about 70% by weight of polytetrafluoroethylene isrequired. These particles have no shape requirement but should be in asize range of from 0.05 to 0.5 micron average diameter, as found incommercial polytetrafluoroethylene dispersions. The higher concentrationlimit is dictated by the rapid viscosity increase of the dispersion withincreasing amount of solid particles. A practical limit. of aboutpolytetrafiuoroethylene particles is about the highest concentration atwhich the viscosity of said dispersion is still suificiently low to makethe composition fluid enough to be pourable and extrudable atsufficiently high pressure within the most economical temperature range.

Temperature.-A preferred range of extrusion temperature for the processof this invention is from about 50 C. to 110 C. The best temperature forextruding a polytetrafluoroethylene dispersion depends on the amount andthe character of liquids in said dispersion. As noted above, betterspinning is obtained at temperatures between about 80 C. and about C.Water may be the sole liquid present or may be mixed with an organicthickener. In either case there is a minor amount of dispersing agentpresent also.

Dispersing agent.The preferred dispersing agents in the composition ofthe instant invention are those present in commercially availablepolytetrafluoroethylene dispersions. Usually ammoniumperfiuorocaprylate, an ionic dispersing agent is used in preparing suchdispersions and Triton X-100, a non-ionic ingredient, is addedsubsequently to the dispersion to keep the particles suspended. TritonX-l00 is miscible with water up to about 30 C., but separates when thetemperature is raised. It is this demixing property which is utilized inthe thermal decantation method of concentrating the commercialdispersion. Thus, ionic and non-ionie dispersing agents may be usedinlimited amounts, to total from about 2% to about 20% by weight of thedispersion. The total quantity of dispersing agents varies with theamount of dispersed polytetrafluoroethylene. Obviously, a dispersingagent, to be useful herein must be a non-coagulant for the suspendedpolymer particles.

Spinnerets.-Shear applied to the spinning mixture increases withdecreasing orifice diameter. The preferred range for such an orificediameter is fromabout 5 to about mils. Shear also'increases withincreasing length of the spinneret shaft, for which the preferred rangeis. from about 0.25 to 1 inch. When shorter needle shafts are used,additional shear may be obtained by inserting a sand pack or a setof'fine screens prior to the spinning cell. For practical purposes, a0.5-.-1.5 inch thick sand pack with. 150 to 200 mesh sand producesadequate additional shear for ordinary spinneret, but thicker sand packsmay be necessary with very short orifice shafts or very large diameterorifices.

The importance of the above conditions is indicated by the fact that afluid polytetrafluoroethylene dispersion within the concentration limitsuseful for the process of this invention, when extruded through anordinary spinneret, either drips out of the spinneret hole or holes, orelse the solid polymer particles plug up the spinneret and no continuousfilament can be obtained. By using a hypodermic needle-type spinneretwithin the above, given dimensions, the same fluidpolytetrafluoroethylene dispersion extrudes intoa continuous.gel-filament of adequate. strength for further handling.

Another type spinneret which can-be used to advantage in this inventionis the split tapered. plug spinneret. This spinneret is especiallysuitable for extrusionunder high pressure and can be easily disassembledfor cleaning purposes. It consists of a ring which is essentially of thesame size as the standard spinneret ring it replaces. The hole in thering is tapered. The plug is split through the center lengthwise andfits the tapered hole. Bosses are left on each side of each plug halfand screws are used to fasten the two halves together. In making theplug, one or more piano wires are laid on one half of the plug, theother half is screwed to it, andthe wholev assembly pressed together.The screws and wires are then removed, the bosses machined off, and thetwo halves, of the plug pressed into the ring, thus completing thespinneret. Allv joints of this split tapered plug spinneret arevself-sealing. The cones can have various lengths and the orificesvarious diameters, depending on the amount of shear necessary for thedesired extruded article. Theoretically, no limit to the length oforifice or orifices exists, but for practical purposes, tapered plugsfrom 0.5 inch to 5 inches length will produce enough shear forvsatisfactory extrusion of shaped articles from the fluid dispersions ofthe present invention. Orifice diameter, varying from about 5 to about15 mils, also produces enough shear.

Dispersed particles.--As stated before, the composition useful for theprocess of the present invention contains preferably between about 45%and about 85% by weight of polytetrafluoroethylene particles. which canvary in size from 0.05 to 0.5 micron average diameter. The shape ofthese particles, is of little importance and a commercialpolytetrafluoroethylene dispersion can easily be used as startingmaterial for the, production of a. composition useful, in the presentinvention. More specifically, rod-like particles asdescribed in US.2,559,-. 750 referred to above are not required. The spinning mixture ofthe invention is fluid, of sufliciently high viscosity to be effectivelyspun, and of a viscosity low enough to permit spinning without plugging.

Bolytetrafluoroethylene dispersions of high concentrations are. made byusing a commercial aqueous dispersion of. the polymer, adding an organicthickener, and

8 removing a substantial portion of the water. This is achieved bythermal decantation or by evaporation of water, for example, atreducedpressure and increased temperature. By such methods there may beobtained a composition containing only a very small amount of water, say1%., which can easily-be shear coalesced'into a gel filament.

Organic thickener.The spinning mixture of this invention preferablycontains an organic thickener in an amount up to about 45 However, asubstantial'proportion of water may be present in the composition and?in fact water may be the sole liquid in the spinning mixture, as long asthe polytetrafluoroethylene particle content is high enough to produce adispersion of'sufiicient viscosity to be effectively spun (i.e., aboveabout 70%). Among the organic compounds which are useful arepolyalcohols,.monoethers and monoesters of polyalcohols, each having atleast two free hydroxy groups, poly(hydroxyalkyl). amines,bis(omega-amino-alkylene) amine carbohydrates,,etc. These liquids haveto be selected such that they are water soluble and do not coagulate andseparate polytetrafluoroethylene particles from an aqueous dispersion.The latter conditions can, of course, be achieved by the addition of awater-soluble dispersing agent which, obviously, has to meet the sameconditions, namely, to be water-soluble, miscible with the organicliquid used as thickener, and a non-coagulant for thepolytetrafluoroethylene particles.

Conversion of a polytetrafluoroethylene dispersion from a fluid,low-pressure filterable state to a firmgel threadline, according to thisinvention, is accomplished by, application of sufficient shear to thepolytetrafluoroethylene particles. This shear generates long fibrilsfromthe original spheroids, present in a commercial polytetrafluoroethylenedispersion with an average diameter of about 0.2 micron. The fibrilsrange in diameter from 0.1.-0.01 micron and show in electron diffractionpat terns an almost perfect orientation. The electron micrographs of theunsintered gel-filament show no free ends; -i.e., the fibrils extendfrom one fibril particle to the next from which another fibril connectsto the following etc., the fibrils. being essentially parallel-alignedfrom the stretch applied during extrusion of the gel-filament. Thesintered filament, however, cannot be distinguished from othercontinuous polytetrafluoroethylene filaments except by; its aesthetic.appearance, its physical properties, and its purity. Such filaments areparticularly characterized bybeing absolutely White, as compared withthe darkercolored filaments of the prior art.

The product of the invention has, due to the nature of thepolymer used,a large number of applications. The white, strong filaments can be spuninto yarns which find their application in high temperature and electricinsulation. The yarns can also be woven into fabrics of excellenthigh-temperature resistance useful as filter cloth for corrosive.liquids at high temperatures, as press pad covers, etc. Of. course, thepresent invention also permits the production of films, ribbons, tapes,etc., as well as. filaments, if.- the shape of the orifice or orificesis changed appropriately. The; filament obtained. by the processof thepresent invention is, carbon free, and is more economical to. producethan prior art polytetrafluoroethylene products, since a purificationstep is not required.

Another advantageof'the; present process is the possibility of spinninglow. denierpolytetrafluoroethylene filaments. Ofcourse, it is possibleto produce the present polytetrafluoroethylene filament in any desiredcolor by adding the desired pigment to the fluid dispersion.Furthermore, the present process operates at high speed, it constitutesacontinuous spinning procedure, it enables the spinning of amultifilament yarn, and operates at low pressure,again advantages overall the known prior art. 7

I claim:

1. The process of forming shaped articles of tetrafiuoroethylenepolymers comprising the steps of providing a mixture comprising fromabout 45% to about 85% by weight of dispersed particles of atetrafiuoroethylene polymer, from about 2% to about 20% by weight of adispersing agent, less than about 45% by weight of a water solubleorganic thickener comprising one of the group consisting ofpolyalcohols, monoethers of water soluble polyalcohols, and monoestersof water soluble polyalcohols, each having at least two free by droxygroups, hydroxyalkyl amines, polyhydroxyalkyl amines, carbohydrates andbis( omega amino alkyl) amines, said mixture being characterized by atotal organic material content of at least about 70%, the remainingproportion being water, and extruding this mixture under shear at leastas high as the shear exerted on the mixture when it is extruded throughan orifice having a diameter of mils and a shaft length of 0.25 inch ata pressure of 1000 pounds per square inch and a polymer temperature of50 C.

2. The process of forming shaped articles of tetrafiuoroethylenepolymers comprising the steps of providing a mixture comprising fromabout 45% to about 85% by weight of dispersed particles of atetrafiuoroethylene polymer, from about 2% to about by weight of adispersing agent, less than about 45 by weight of a water solubleorganic thickener comprising one of the group consisting ofpolyalcohols, monoethers of water soluble polyalcohols, and monoestersof water soluble polyalcohols, each having at least two free hydroxygroups, hydroalkyl amines, polyhydroxyalkyl amines, carbohydrates andbis(omega-amino-alkyl) amines, said mixture being characterized by atotal organic material content of at least about 70%, the remainingproportion being water, and extruding this mixture through an orificehaving a diameter of from about 5 to about 15 mils and a shaft length offrom about 0.25 inch to about 5 inches, at a pressure of from about 1000pounds per square inch to about 5500 pounds per square inch and at apolymer temperature between about 50 C. and about 110 C., whereby ashaped article is formed.

3. The process of claim 2 wherein the polymer temperature is from aboutC. to about C.

4. The process of claim 2 including the additional step of sintering theresulting shaped article at a temperature between about 375 C. and about430 C.

5. The process of claim 2 wherein the mixture is extruded at aspin-stretch factor of up to about 1:5.

6. The process of claim 4 wherein the mixture is extruded at aspin-stretch factor of up to about 1:5.

7. The process of claim 5 wherein the spin-stretch factor is betweenabout 1:15 and about 1:2.

8. The process of claim 2 including the additional step of washing theresulting shaped article to remove organic material other than thepolytetrafluoroethylene particles.

9. The process of claim 7 wherein the shaped article is washed withacetone.

10. The process of claim 2 wherein the mixture passes through a sandpack prior to extrusion through the orifices.

11. The process of claim 9 wherein the sand pack is from about 0.5 inchto about 1.5 inches in length.

12. The process of claim 2 wherein the mixture is extruded through ahypodermic-needle type spinneret assembly having orifices of from about5 to about 15 mils diameter with a spinneret shaft length of from about0.25 to about 1 inch.

13. The process of claim 2 wherein the mixture is extruded through atapered-plug type spinneret assembly having an orifice of from about 5to about 15 mils diameter with a spinneret shaft length of from about0.5 to about 5 inches.

14. The process of claim 2 wherein the shaped article is 'a continuousfilament.

References Cited in the file of this patent UNITED STATES PATENTS2,266,363 Graves Dec. 16, 1941 2,413,498 Hill Dec. 31, 1946 2,718,452Lontz Sept. 20, 1955 2,772,444 Burrows et a1. Dec. 4, 1956 2,824,780Satterthwaite Feb. 25, 1958 2,829,944 Houtz et al. Apr. 8, 19582,881,142 Eldridge Apr. 7, 1959

1. THE PROCESS OF FORMING SHAPED ARTICLES OF TETRAFLUOROETHYLENEPOLYMERS COMPRISING THE STEPS OF PROVIDING A MIXTURE COMPRISING FROMABOUT 45% TO ABOUT 85% BY WEIGHT OF DISPERSED PARTICLES OF ATETRAFLUOROETHYLENE POLYMER, FROM ABOUT 2% TO ABOUT 20% BY WEIGHT OF ADISPERSING AGENT, LESS THAN ABOUT 45% BY WEIGHT OF A WATER SOLUBLEORGANIC THICKNESS COMPRISING ONE OF THE GROUP CONSISTING OFPOLYALCOHOLS, MONOETHERS OF WATER SOLUBLE POLYALCOHOLS, AND MONOESTERSOF WATER SOLUBLE POLYALCOHOLS, AND MONOESTERS OF WATER DROXY GROUPS,HYDROXYALKYL AMINES, POLYHYDROXYALKYL ANIMES, CARBOHYDRATES ANDBIS(OMEG - AMINO - ALKYL) AMINES, SAID MIXTURE BEING CHARACTERIZED BY ATOTAL ORGANIC MATERIAL CONTENT OF AT LEAST ABOUT 70%, THE REMAININGPROPORTION BEING WATER, AND EXTRUDING THIS MIXTURE UNDER SHEAR AT LEASTAS HIGH AS THE SHEAR EXTENDED ON THE MIXTURE WHEN IT IS EXTRUDED THROUGHAN ORIFICE HAVING A DIAMETER OF 15 MILS AND A SHAFT LENGTH OF 0.25INCHES AT A PRESSURE OF 1000 POUNDS PER SQUARE INCH AND A POLYMERTEMPERATURE OF 50*C.